The present invention relates to a method for generating and analyzing radar pulses, in particular for short-range pulse radar applications in motor vehicles.
In automotive engineering, radar sensors are used to measure the distance to objects and/or the relative speed of such objects outside the motor vehicle. Objects may include, for example, motor vehicles driving ahead or parked motor vehicles, pedestrians, cyclists, or installations in the vicinity of the motor vehicle.
FIG. 1 shows a schematic representation of a radar device with the correlation receiver of the related art. A transmitter 300 is induced by a pulse generator 302 to emit a transmit signal 306 via an antenna 304. Transmit signal 306 strikes a target object 308, where it is reflected. Receive signal 310 is received by antenna 312. This antenna 312 may be identical to antenna 304. After receive signal 310 is received via antenna 312, it is transmitted to receiver 314 and is subsequently supplied to a signal analyzer 318 via a unit 316 having a lowpass and an analog/digital converter. The characteristic feature of a correlation receiver is that receiver 314 receives a reference signal 320 from pulse generator 302. Receive signals 310 received by receiver 314 are mixed with reference signal 320 in receiver 314. By correlation, it is possible to infer, for example, the distance to a target object on the basis of the time delay between transmission and reception of the radar pulses.
A similar radar device is described in German Published Patent Application No. 199 26 787. A transmission switch is switched on and off by the pulses of a generator so that during the pulse duration, a radio frequency wave generated by an oscillator and guided to the transmission switch via a branching is switched through to the transmitting antenna. A receiving component also receives the output signal of the generator. The receive signal, i.e., a radar pulse reflected by an object, is mixed with the oscillator signal which reaches a mixer via a receive switch during a pre-set time. U.S. Pat. No. 6,067,040 also operates with a transmission switch that is switched on and off by pulses of a generator. For the reception of the reflected radar pulses, separate channels for 1 and Q signals are provided. In this case also, the receive signal is mixed and analyzed only during a pre-set time.
The measures of the present invention make it possible to detect objects reliably. In contrast to the devices and methods known heretofore, noise problems play only a minor role. In addition, some RF components such as radio frequency switches are eliminated, permitting a simpler, less costly and consequently more cost-effective implementation of a radar sensor.
The present invention makes a radar concept possible which shifts to the LF or IF side the required rapid switching in the range of several hundred ps to detect objects in the vicinity of a motor vehicle, the switching occurring on the RF side in conventional SRR (short range radar). It is possible to combine the mixing and switching function in one component.
The concept according to the present invention requires only one antenna, which is used to transmit and receive radar pulses simultaneously. This essentially reduces the sensor size. In the method according to the present invention, a continuous signal of a radio frequency source may be connected with an antenna via at least one mixer. To generate a radar pulse, the mixer is briefly brought into a state of low throughput loss. The signal of the radio frequency source is then able to pass the mixer and reaches the antenna. Immediately after the radar pulse is generated and transmitted, the mixer is switched over to receive mode and awaits the return of the transmitted radar pulse which is reflected by an object. The delay time is a measure of the distance of the object. Upon receiving the radar pulse, the mixer, together with the continuous signal of the radio frequency source, generates an LF or IF pulse representing the envelope of the RF pulse and is capable of being analyzed.
With the present invention, it is possible to increase the detection range of a radar sensor at a working frequency of 24.125 Ghz to as much as 100 meters since the receive signals of the objects to be detected are not lost in noise as a function of the object characteristics as is ordinarily the case. This makes it possible to detect objects reliably.
In order to attain I/Q capability of the radar, two mixers may be interconnected for the inphase (I)-IF signal and the quadrature (Q)-IF signal.
The mixer or mixers may be placed into the state of low throughput loss, so that the intermediate frequency output of the mixer or mixers is connected to a power source. The resulting mixed signalxe2x80x94IF output signal of the mixerxe2x80x94may be amplified and sampled at a high bandwidth.
The mixed signal may be amplified and scanned separately for the I and Q IF signal.
To sample the mixed signal, a very short sampling pulse may be applied to a broadband sampler, the time of which corresponds to a selected distance cell.